The pharmaceutical industry spends billions of dollars every year in preclinical and clinical research in its quest for new therapeutics. A potential therapeutic must be assessed and approved for clinical efficacy and safety before it can be marketed. In cases where a drug entity is being evaluated for treatment of a condition where there is no conventional therapy available for treatment, the new drug is generally compared with a placebo. A placebo is a mixture lacking any active ingredients. Generally, the placebo is made to look similar to the “real” treatment. Clinical trials are structured to comprise a drug treatment group and a placebo treatment group. Typically, the clinical investigators and the subjects of the trial are blinded to the assignment of subjects in these groups.
It has been discovered that individuals receiving placebo treatments often experience an improvement in their condition, or alternatively, can experience side effects similar to those exhibited by individuals receiving drug treatment. Such a reaction to an “inert” treatment i.e. a treatment lacking an active ingredient is termed the “placebo effect”. The placebo effect is common in medicine. It has been suggested that four out of ten people will feel some improvement as a result of taking a placebo. Theorists have attributed the placebo effect to have some sort of a psychological or physiological bases. However, it is likely that the physiological manifestation of the placebo effect is at least in some cases triggered by natural responses of the human body.
Some believe the placebo effect is psychological in nature, brought about by a belief in the treatment, or a perception with respect to a subjective feeling of improvement. For example, it has been postulated that the effectiveness of some drugs may be attributed almost entirely to the placebo effect. In one analysis of 19 clinical trials of antidepressants, the authors concluded that the expectation of improvement, not adjustments in brain chemistry, accounted for 75 percent of the drugs' effectiveness (Kirsch et al. (1998) “Listening to Prozac but Hearing Placebo: A Meta-Analysis of Antidepressant Medication” Prevention & Treatment, Volume 1, Article 0002a. In an earlier study, Sapirstein analyzed 39 studies, done between 1974 and 1995, of depressed patients treated with drugs, psychotherapy, or a combination of both. He found that 50 percent of the drug effect is due to the placebo response.
The placebo effect has also been used as an explanation for the apparent benefits of certain complementary therapies where patients are sure they feel better after having therapy, even where there is no scientific evidence that the therapy has any effect on their illness.
It would be useful to understand cause(s) of the placebo effect and to predict their occurrence before including a given individual in a clinical trial. Understanding and/or being able to predict placebo effects could help in filtering out noise in clinical trials and in avoiding flawed study designs. It would be a significant benefit to the pharmaceutical industry if one could simply avoid or reduce the impact of the placebo effect on the data derived from a clinical trial.